(1) Field of the Invention
The invention relates to sensor-controlled deburring of metallic workpieces, in particular the cleaning of castings by face milling, in which process the axis of a tool is tilted relative to a normal line on the surface of a base material of a workpiece, the tool and workpiece being electrically isolated from one another. An electrical voltage is applied at least between one part of the tool and the workpiece. The tool engages with the workpiece under numerical control. The time of contact of a cutting edge with the workpiece is evaluated independently of the speed of the tool during its control as a measure of the width of the tool mark and thus the penetrating depth of the tool when deburring relatively small flashes.
The invention also relates to a cutting sensor for conducting sensor-controlled deburring of metallic workpieces, in particular of castings of the aformentioned kind. The cutting sensor is formed by a workpiece, a sensor cutter that engages with the workiece and whose longitudinal axis is sloped relative to the normal line on the surface of the base material of the workpiece, and an evaluating unit connected to the sensor cutter. The workpiece or the sensor cutter is electrically isolated from its environment and has a measurement voltage applied thereto.
(2) State of the Prior Art
Castings are fraught with tolerances. The cast blanks are far from being at a required defined geometry owing to gating systems and flashes of various shapes and heights. Therefore, the castings must be deburred and smoothed by cleaning. This is predominantly done manually, since acceptable machining results are obtained only in exceptional cases when castings are cleaned automatically, owing to defective compensation for tolerances.
For automatic cleaning of castings with numerically controlled (NC) machine tools, the object is to follow the contour of the workpiece and remove the gating systems and flashes.
Since the flashes vary in shape, width and height with large tolerances, a constantly high cleaning quality can be achieved in numerically controlled automated procedures only with sensors. They monitor the deviation of the actual shape of the flash and its position from a predetermined tolerance value and must correspondingly correct the deburring process.
Previous attempts started from force measurements, performance measurements and optical measurements. None of these principles led to results that would be comparable to those of a cutting sensor. With a cutting sensor it is possible to measure these deviations directly and to compensate with suitable procedures. A known sensor-controlled deburring of the aforementioned kind (M. Weck and J.-P. Furba, VDI-Z., Vol. 128 (1986), no. 22, pp. 879-883) has been proven to have the drawback that it no longer functions when there are large bent-over flashes. If in the case of relatively high flashes, the cutter bends over during this contact measurement, the contact time is no longer determined by the base material but rather by the bent over flash. In this manner the automatically guided sensor cutter is led astray.